How to connect a DSP using the digital audio output
There are two digital outputs. The optical SPDIF socket is on the rear panel of the unit, and a coaxial SPDIF output sits on C6 of Harness C on a brown wire. Use whichever one your processor has an input for. Neither is needed for a standard install.
What this gives you
The signal reaches the processor without ever becoming analog, so the tuning happens on the numbers rather than on top of whatever the RCA run picked up on the way. In a vehicle with a long cable run down the transmission tunnel to a rear mounted processor, that run is where noise gets in.
Before you start
- A processor with an optical or a coaxial SPDIF input. Check which before you buy a lead.
- For optical, a Toslink lead routed without a tight bend. Optical fibre does not like being kinked behind a dash.
- For coaxial, Harness C, which is supplied, and a 75 ohm coaxial lead to the processor.
- The processor already powered and earthed, since the head unit only sends signal.
Step by step
- Decide which output the processor can actually take
Optical and coaxial carry the same signal. It is only the socket that differs, so the processor decides this, not the head unit.
- For optical, use the rear panel socket
The SPDIF digital audio output is one of the nine connections on the rear panel of the unit, alongside the HDMI output and the antenna connections. Plug the Toslink lead in before the unit goes back into the dash, because it is not reachable afterwards.
- For coaxial, use C6 on Harness C
C6 is the coaxial digital output and the wire is brown. It is a different output to the optical one on the rear panel, not the same signal split two ways.
- Route the lead where it will not get crushed
Behind the fascia is tight once the unit goes back. Run the lead first, check the unit still seats flush at all four corners, then tidy it.
- Set the processor input to digital
A processor left on its analog input will find nothing on the digital one. This is the step that makes a working install look like a dead output.
- Decide whether you still need the pre-outs
If everything is going through the processor, the analog pre-outs on Harness A and Harness C are spare. If part of the system is still running on analog, they stay.
If it does not work
- Nothing at the processor: check the processor is switched to its digital input first, before you touch anything at the head unit end.
- Optical showing no light: a Toslink lead glows faintly red at the end when it is live. No light means the lead, the socket or a kink in the run.
- Audio drops in and out on coaxial: check the lead is a proper 75 ohm coaxial lead rather than a standard RCA audio lead, which is not the same thing.
- Sound but no control: the processor is passing the signal through untuned. That is a processor setting, not a wiring fault.
Worth knowing
C6 sits next to the 5.1 centre channel output on C2 and the rear pre-outs on C3 and C4, so the same harness can feed a processor digitally and an amplifier on analog at the same time.
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